Standards for an optical signal for realizing large-capacity and long-haul communication are defined in the Optical Transport Network (OTN) as specified in ITU-T G.709. Among those, an OTN maintenance signal is formed of, for example, a repeating pattern such as ODU AIS (all “1”s), OCI (repeating “0110”), or LCK (repeating “0101”). In addition, in order to prevent signal degradation on a transmission path, such an OTN maintenance signal is specified to be subjected to scrambling operation before being output (see, for example, Non Patent Literature 1).
Further, there is disclosed an example of a 100 G long-haul transceiver for performing error correction processing for long-haul transmission and transmitting and receiving a polarization multiplexed QPSK signal (see, for example, Non Patent Literature 2).